Maladjustment of β-CGRP/α-CGRP Regulation of AQP5 Promotes Transition of Alveolar Epithelial Cell Apoptosis to Pulmonary Fibrosis.

This study explored the triggering mechanism of interstitial lung disease (ILD). We established the effects of immunogenic and neurogenic calcitonin gene-related peptide (CGRP) imbalance on the regulation of aquaporin 5 (AQP5) expression and the repair responses that promote the transition from alveolar epithelial cell (AEC) apoptosis to pulmonary fibrosis. Newly diagnosed ILD patients (n = 60) were enrolled, whose serological levels of beta-CGRP, alpha-CGRP, AQP5, receptor activity modifying protein 1, and receptor component protein were detected by ELISA. Th1 and Th2 cytokines and CD4(+)and CD8(+)cells were measured by flow cytometry method.In vivo, bleomycin (BLM) was set for modeling pulmonary fibrosis. ACALCA-HET model was set as a chronic pulmonary fibrosis model. Hematoxylin-eosin, immunohistochemistry, and Masson's trichrome staining were performed to assess the role of apoptosis in the injured lung. The concentrations of cytokines were determined by cytokine antibody arrays. Abnormal activation of serological CD4(+)T lymphocytes and predominant Th2 response was established in the patients with ILD. Moreover, the ratio of beta-CGRP/alpha-CGRP positively correlated with the increased level of AQP5 in patients with ILD.In vivo, a significant increase of AQP5 and beta-CGRP at the chronic stage of pulmonary fibrosis was induced by BLM in the mice model, whereas the expression of AQP5 protein was generally lower in the acute alveolitis phase. Moreover, the levels of AQP5 and alpha-CGRP in theCALCA-HET rats were lower than those of the normal saline group. The high ratio beta-CGRP/alpha-CGRP enhanced the expression of AQP5, inhibited transforming growth factor-beta 1 (TGF beta 1)/P-Smad1/Smad4 pathway, and upregulated the NRF2 signal, whereas the apoptosis of AECs was significantly reduced in late-stage pulmonary fibrosis. The imbalance of beta-CGRP/alpha-CGRP may be associated with the predominance of Th2 response and participate in the process of AEC apoptosis in lung fibrosis. The high ratio of beta-CGRP/alpha-CGRP may elevate the level of AQP5 through inactivation of the TGF-beta 1/smad1 signaling pathway and upregulation of the Nrf2 signaling in the chronic stage of pulmonary fibrosis.